As a display method for presenting information to a driver of a vehicle, a variety of methods are proposed. One of the conventional methods is a head-up display (HUD). This HUD apparatus is characterized in that the HUD is capable of reducing the quantity of movement of the user's point of sight and, hence, useful for safety enhancement.
In order to improve the display visual recognizability of the HUD apparatus, a display apparatus disclosed in Japanese patent 2,913,901 has been proposed as a display apparatus utilizing a difference in vision between the eyes of the driver. According to this display apparatus, the difference in vision, amount and position of display data are varied in accordance with changes in vehicle traveling position to improve the perception ability of the driver and to enhance safety.
However, this display apparatus does not show a display according to the condition of the environment external to the vehicle. As a result, the ability of the display apparatus to present a visually recognizable display may deteriorate due to the condition of the external environment in some cases. When a guiding arrow leading ahead of the vehicle by a distance of 100 m is shown by using the difference in vision between the eyes of the driver as a three-dimensional display, it is likely that the driver hardly recognizes the guiding arrow leading ahead of the vehicle by a distance of 100 m because the driver pays attention to another vehicle leading ahead of this vehicle by a distance of 20 m.